This invention relates to pumps, and more particularly, to a piston-type pump for pumping material such as a lubricant, and especially for pumping a relatively high viscosity lubricant such as wheel bearing grease.
This invention involves an improvement in pumps of the type such as shown for example in U.S. Pat. Nos. 1,970,591 and 2,057,874, generally comprising a pump tube, having an inlet at one end (its lower end), an outlet at its upper end, a valved piston slidable in the tube, and a valve for the inlet, the latter valve opening on an upstroke of the piston for priming of the pump tube and closing on a downstroke of the piston for forcing material from below the piston through the piston (the valve in the piston opening for this purpose) to the tube above the piston. Pumps of this type, and such as shown in said patents, have generally been satisfactory for pumping materials (e.g., lubricants), but may present the problem when used for pumping lubricants or other materials of high viscosity such as wheel bearing grease, of losing prime due to the difficulty attendant upon flow of the high viscosity material through the inlet into the tube. In pumps of this type, the vacuum developed at the inlet during the piston upstroke to draw lubricant into the tube develops gradually and may not be wholly effective to overcome the resistance to flow of high viscosity lubricant into the pump tube below the piston, thereby causing priming problems.